CN113166984A

CN113166984A - Environmentally responsive bicomponent microfiber textiles and methods of making same

Info

Publication number: CN113166984A
Application number: CN201980075643.3A
Authority: CN
Inventors: 王宇皇; 彭志伟; 许蓓蓓; 贝南·波尔帝希米; 阿巴伊·乔伊乔德
Original assignee: North Carolina State University; University of Maryland at College Park
Current assignee: North Carolina State University; University of Maryland at College Park
Priority date: 2018-10-16
Filing date: 2019-04-30
Publication date: 2021-07-23
Also published as: WO2020081121A1; EP3867430A4; EP3867430A1; US20210372014A1

Abstract

Biconstituent fibers are formed into an eccentric sheath-core configuration or a side-by-side key-lock configuration by spinning two antagonistic polymer melts, one of which contains pre-compounded optical nanostructures. The bi-shaped meta-fiber is capable of adaptively adjusting infrared radiation in response to a deviation in humidity level from a comfort zone or perspiration level of a wearer of a garment made from the meta-fiber. The bi-modal fiber is moisture/heat trained to achieve a dynamic environmental response behavior to maintain a moisture/heat comfort zone under various moisture level fluctuations.

Description

Environmentally responsive bicomponent microfiber textiles and methods of making same

Statement regarding federally sponsored development research

The invention was made with government support in accordance with DEAR0000527 awarded by DOE ARPA-E. The government has certain rights in this invention.

Reference to related patent applications

The utility patent application is based on provisional application No. 62/746,347 filed on 16/10/2018.

Technical Field

The present invention relates to smart materials for energy conservation and environmental response, and in particular to the production of composite textile materials capable of self-regulating the heat exchange between the wearer's body and the environment.

The invention also relates to the manufacture of intelligent textiles from bi-shaped elementary fibers capable of self-adjusting the infrared emissivity of the textile to a thermal/humidity comfort zone in response to environmental parameter fluctuations.

In a general concept, the present invention relates to a smart textile made from a yarn containing bi-modal elementary fibers formed by spinning two antagonistic polymeric (hydrophobic and hydrophilic) components, wherein optical nanostructures are embedded in at least one polymeric component, and the yarn is thermally trained (shaped) in a predetermined heat/humidity dypa zone to achieve properties of environmental response through modulation of electromagnetic coupling between the optical nanostructures in the fibers, such that self-regulation of heat transport in the smart textile is maintained in the heat/humidity comfort zone.

In addition, the present invention relates to the manufacture of wearable garments from bi-shaped meta-fibers embedded with selected optical nanostructures incorporated in the fiber, and the behavior to demonstrate a dynamic humidity response due to effective electromagnetic coupling with self-tuning of the optical nanostructures.

The invention also relates to a single-step spinning process for manufacturing a meta-fiber based material having tunable infrared emissivity and heat transfer adjustability in response to ambient humidity fluctuations in order to maintain a thermal comfort zone of the wearer without external power consumption.

Background

Energy conservation is an important issue in the development of human society and civilization. In the united states, about 40% of the total energy produced is consumed by residential and commercial buildings. Approximately 37% of the energy consumed is used for heating and/or cooling in order to maintain thermal comfort for the occupants of the building. Such energy consumption for heating or cooling of a large volume of space of a building results in substantial energy waste, which brings about harmful global climate change.

In view of such problems, there is a great commercial interest in developing wearable garment technologies that can provide a comfort zone for the wearer of the garment, which will reduce the large energy consumption for environmental control in buildings.

The use of such clothing technologies may be more beneficial in places other than homes or office buildings, such as in harsh working environments, for example, battlefields or hot and humid industrial environments. In these extreme environments, regulation of body temperature and heat transfer through the wearer's clothing will be extremely important for the survival of people exposed to such harsh environmental conditions.

Textile materials for the environmental response of garments may also be beneficial for enhanced care of infants and medical patients who need personal attendance to meet their thermal comfort needs.

Bicomponent fibers are made with two antagonistic polymers having different chemical and/or physical properties. In the manufacturing process, the two polymers are extruded from the same spinneret, with both polymers in the same filament.

The difference in shrinkage between the resistant polymers in the bicomponent fiber caused by environmental stimuli such as heat and/or humidity fluctuations results in a strong environmental response of the bicomponent fiber.

Examples of commercial products based on bicomponent fibers include AeroReactTM by Nack and VentcoolTM by Mitsubishi Yang, which use perspiration responsive fabrics designed to maintain the wearer's skin dry by increasing the air space in the textile to promote perspiration wicking. However, these techniques are neither capable of active adjustment of infrared radiation (which is the primary heat transfer pathway for heat dissipation from the human body to the environment), nor active dynamic tuning of infrared emissivity to self-adjust heat transfer in response to environmental changes.

Infrared garments are commercially available that incorporate nanoparticles to enhance the absorption of infrared radiation useful for hyperthermia therapy. However, the prior art is passive and therefore not capable of self-regulating heat transfer by infrared radiation.

It would be highly desirable to further develop intelligent textiles fabricated from bicomponent microfibers that are capable of self-regulating heat transfer to a predetermined thermal/humidity comfort zone in response to environmental deviations from the predetermined thermal/humidity comfort zone via active modulation of Infrared (IR) radiation and dynamic adjustment of IR emissivity as a heat transfer channel.

Disclosure of Invention

It is therefore an object of the present invention to provide a composite material made of bicomponent fibers incorporating optical nanostructures, configured with an optical coupling mechanism capable of actively tuning the infrared emissivity in response to environmental changes.

It is another object of the present invention to provide a smart textile capable of providing self-regulating thermal comfort to the wearer of a garment made from the smart textile, the smart textile being made from bicomponent meta-fibers incorporating optical nanostructures.

It is yet another object of the present invention to make smart textiles from bicomponent (antagonistic polymeric component) fibers that are capable of dynamic mechanical changes due to differences in hygroscopicity of the antagonistic polymers (one hydrophilic and the other hydrophobic) and demonstrate actively tunable infrared emissivity resulting from modulation of electromagnetic coupling of optical nanostructures embedded in the hydrophobic component of the fiber, caused by dynamically changing displacements of adjacent fibers, with the aim of maintaining the wearer's comfort zone in varying environments.

It is an additional object of the present invention to provide a smart textile formed of composite fibers fabricated with at least two physically distinct base polymers and optical nanostructures embedded therein to enable a meta-cooling textile (MCT) technology that will be able to modulate the infrared emissivity of the textile in response to thermal discomfort, thus providing thermal regulation in a self-powered manner (without requiring additional power to maintain thermal comfort).

Furthermore, it is an object of the present invention to manufacture a smart textile from composite fibers that enable dynamic tuning of infrared radiation (as the primary channel of heat transfer through the textile) and energy exchange between the wearer's body and the surrounding environment, thus providing efficient localized thermal management.

The present invention is also directed to a humidity-responsive bicomponent fibril fabricated from a polymeric composite having optical nanostructures incorporated therein that curl or straighten depending on relative humidity and/or perspiration level, thus modulating the relative positioning of the optical nanostructures in adjacent fibrils to control electromagnetic coupling between the optical nanostructures in adjacent fibrils and modulate thermal radiation in the infrared range.

Further, it is an object of the present invention to provide a composite fiber capable of reversible self-regulation of the heat transfer mechanism, wherein an increase or decrease of the humidity level causes straightening or curling, respectively, of the meta-fiber, which results in modulation of the relative displacement between adjacent meta-fibers, resulting in an enhanced or reduced infrared emissivity of the meta-fiber, which in turn results in a modulation of the heat transfer through the meta-fiber.

It is a further object of the present invention to provide a melt spinning process for the production of meta-cooled fibres by process steps comprising: (a) the optical nanostructures are precompounded into a hydrophobic polymer precursor, followed by (b) direct spinning of the hydrophobic polymer precursor with a antagonistic (hydrophilic) humidity responsive polymer precursor through a spinning head configured to form various configurations of bicomponent fibril fibers capable of dynamic humidity response and self-regulating infrared emissivity.

It is a further object of the present invention to provide a thermal "training" process to define an "open" state of the meta-cooling fiber under wet conditions, wherein the fiber is straightened to reduce the relative positioning of adjacent fibers to allow maximum electromagnetic coupling between optical nanostructures in adjacent fibers, followed by a thermal "training" step to define a "closed" state of the meta-cooling fiber under dry conditions, wherein the fiber is crimped to increase the relative positioning of adjacent fibers to achieve minimum electromagnetic coupling between optical nanostructures in adjacent fibers.

It is a further object of the present invention to provide a scalable manufacturing process for producing primary cooling fibers and textiles by the steps of: (a) compounding an optical nanostructure with a polymer melt, (b) melt spinning of bicomponent fibers, and (c) heat setting (training) to produce a dynamic humidity response of the meta-cooling fiber.

It is yet another object of the present invention to produce energy-saving and environmentally responsive composite fibers for various applications, particularly for wearable humidity-responsive apparel technologies on the body, sports apparel, medical and military apparel, and infant apparel, to achieve efficient and rapid self-cooling of the apparel, and for wearable technologies adapted to harsh working environments that enable effective self-regulation of heat transfer from the wearer's body.

In one aspect, the present invention relates to smart textiles manufactured from meta-fibers. The microfibers in the smart textile are manufactured as bicomponent fibers configured with first and second relatively resistant polymer components, one of which is a hydrophobic polymer component and the other of which is a hydrophilic polymer component. The hydrophobic and hydrophilic polymer components are combined in each bicomponent fiber in an eccentric sheath-core arrangement or in a side-by-side (bond-lock) arrangement. In the eccentric sheath-core structure and arrangement, the hydrophilic polymer serves as the sheath and the hydrophobic polymer serves as the core.

The base bicomponent fiber further comprises optical nanostructures dispersed in the hydrophobic polymer matrix for supporting electromagnetic coupling between the optical nanostructures in adjacent component fibers. The electromagnetic coupling is determined by the distance (pitch) between the fibers and determines the ir emissivity of the composite fabric (smart textile).

In one embodiment, the bicomponent fiber of the present invention comprises a mechanism of moisture response ensured by a moisture responsive polymer.

The mechanism of humidity response operates as follows:

(a) when the relative humidity applied to the meta-fibers is above a predetermined relative humidity level (also referred to herein as the comfort zone), the hydrophilic component of the meta-fibers absorbs moisture, causing the meta-fibers to straighten. The elementary fibers are arranged in the yarn. As the fibers in each yarn are reinforced, the spacing between adjacent fibers decreases, which results in an increase in electromagnetic coupling between the optical nanostructures, thus increasing ir emissivity and enhancing heat transfer due to resonant electromagnetic coupling between optical structures on adjacent element fibers;

(b) however, when the relative humidity applied to the meta-fiber is below a predetermined relative humidity level (comfort zone), the hydrophilic component of the meta-fiber releases moisture, causing curling of the meta-fiber, thereby increasing its adjacent spacing within the yarn, thereby reducing ir emissivity and reducing heat transfer.

The optical nanostructures are embedded in the hydrophobic component of the fibril by compounding the optical nanostructures at the desired concentration prior to the spinning process. It is contemplated that the optical nanostructures included in the meta-fiber of the present invention may comprise single-walled Carbon Nanotubes (CNTs), double-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanohorns, carbon fibers, graphene oxide, carbon black, silver nanowires, copper nanowires, silicon nanowires, gold nanoparticles, and combinations thereof.

Moisture responsive polymers contemplated for use in the present invention can include nylon 6, nylon 66, cellulose, cotton, polyurethane and derivatives thereof, and combinations thereof.

The hydrophobic polymer may comprise polyethylene, polyethylene terephthalate, polypropylene, polybutylene terephthalate, and derivatives thereof, and combinations thereof.

In another aspect, the present invention relates to a method of manufacturing a composite fibril material having a self-regulating ir emissivity in response to ambient humidity fluctuations, comprising the steps of:

(a) the optical nanostructures are compounded into a hydrophobic polymer,

(b) the fibril is formed by direct spinning of two antagonistic molten polymer components (a hydrophilic polymer component and a hydrophobic polymer component) of a double spinneret,

(c) a plurality of elementary fibers are arranged into a yarn, an

(d) The meta-fiber is heat set (trained) to an "open" state in wet conditions, and a "closed" state in dry conditions. When the trained meta-fibers are exposed to fluctuating environmental conditions, depending on the humidity deviation from the predetermined comfort zone, the trained meta-fibers change their configuration, as the thermal training process "dictates", and thus modulate the spacing between adjacent fibers. This changes the electromagnetic coupling between the optical nanostructures and thus adjusts the IR emissivity to control heat transfer between the wearer's body and the environment.

These and other objects and advantages of the present system and method will become more apparent from the following detailed description of the invention when read in conjunction with the accompanying patent drawings.

Drawings

Fig. 1A to 1F are representations of MCT fibers of the present invention with self-regulating ir emissivity, showing a mechanism for enhanced or reduced heat transfer under different humidity conditions, wherein fig. 1A and 1B show the bent and reinforced configurations of the fibers, respectively, fig. 1C and 1D show enlarged and reduced spacing between fibers in the yarn, respectively, and fig. 1E and 1F show textiles formed from dry (reduced distance between yarns) and wet (increased distance between yarns) fibers/yarns, respectively;

FIG. 2 is a schematic diagram of a direct twin form spinning system of the present invention for producing the meta-cooling fiber of the present invention;

FIGS. 3A-3B are schematic diagrams of the system of the present invention in an alternative spinning configuration for meta-cooling fibers, resulting in a side-by-side configuration (FIG. 3A) and an eccentric core-sheath configuration (FIG. 3B);

fig. 4A to 4D are optical and SEM images of cross-sections of the inventive meta-cooling fiber produced by the direct spinning process of the present invention, wherein fig. 4A and 4C are optical and SEM images, respectively, of a side-by-side meta-cooling fiber, and fig. 4B and 4D are optical and SEM images, respectively, of an eccentric sheath-core meta-cooling fiber;

fig. 5A to 5D are SEM images of the meta-cooling fiber of the present invention having an eccentric sheath-core structure, wherein fig. 5A is a top view of a cross-section of the meta-cooling fiber of the present invention having an eccentric sheath-core structure, fig. 5B is an enlarged image of a core region, fig. 5C is a side view image of a split meta-cooling fiber of the present invention having an eccentric sheath-core structure, and fig. 5D is an enlarged side view image of a core region showing a uniform distribution of embedded carbon nanotubes as a meta-element;

FIG. 6 is a graph showing the Raman spectral distribution of the core component of the element cooling fiber of the present invention in a core-sheath configuration;

FIG. 7 is a photograph of a collection spool of meta-cooled yarn incorporating different concentrations of carbon nanotubes (left to right) loaded in the hydrophobic polymer component at 0, 100, 250, 500, 750, and 1000ppm, respectively;

figures 8A to 8B are photographs of knitted fabrics using the element cooling yarn of the present invention, wherein figure 8A is a photograph of a circular knitted MCT fabric (from top left to bottom right, carbon nanotubes loaded in the hydrophobic component are 0, 100, 250, 500, 750 and 1000ppm, respectively), and figure 8B is a photograph of a double knitted MCT fabric with PET fibers;

FIGS. 9A-9B are schematic diagrams showing the mechanism for sizing (training) of a collection of meta-cooling fibers to define a "closed" state in dry conditions for a side-by-side configuration (FIG. 9A) and an eccentric core-sheath configuration (FIG. 9B);

FIGS. 10A through 10C are optical images of the element-cooled fiber of the present invention showing the behavior of the moisture response after the heat-setting step; and

fig. 10D is a graph showing yarn diameter versus relative humidity.

Detailed Description

The present meta-cooling fiber is envisioned as the basis for energy saving and environmentally responsive garments made from smart composites that are capable of actively maintaining a thermal/humidity comfort zone for wearers of such garments, wherein heat transfer from the wearer's body is self-regulating based on changes in infrared radiation in response to ambient humidity fluctuations, and wherein a humidity response mechanism is implemented to maintain the garment in a temperature/humidity comfort zone.

Referring to fig. 1A through 1F, a meta-fabric 10 of the present invention is arranged into yarns 12 that are further knitted into a smart textile (fabric) 14.

The human body primarily absorbs and loses heat through infrared radiation with a peak at about 10 μm (Owen, m.s., 2009Ashrae manual: principles, American Society of Heating, reforming and Air-Conditioning Engineers, inc.: 2009). The present meta-cooling fiber 10 forming the smart fabric 14 uses an IR radiation based heat transfer mechanism for maintaining a thermal comfort zone for the wearer of a garment formed from the smart textile 14 of the present invention by self-regulating the IR emissivity in response to changes in ambient humidity and/or perspiration levels.

Optical nanostructures 16 are embedded in the fibril 10. The weight of the optical nanostructures 16 may be in a range selected from the group of: 0.0025 to 0.03%, 0.005 to 0.05%, and 0.01 to 0.5% by weight of the hydrophobic component 30 in the meta-fiber 10. The meta-cooling fiber 10 of the present invention operates by modulating its infrared emissivity by varying the electromagnetic coupling between optical nanostructures 16 embedded in adjacent meta-cooling fibers 10 within each yarn 12.

Referring to fig. 1A, 1C and 1E, when the humidity in the environment is low (dry environment or low perspiration level), the elementary fibers 10 curl (as shown in fig. 1A) and thus reach a larger inter-fiber distance (pitch) 18, thus effectively reducing the electromagnetic coupling between the optical nanostructures 16 in adjacent elementary fibers 10. The reduced electromagnetic coupling results in less infrared radiation, i.e. reduced heat transfer at low humidity levels in dry conditions.

As the humidity in the environment increases, the elementary fibers 10 straighten (as shown in fig. 1B, 1D, 1F) while reducing the inter-fiber spacing 18 between the fibers 10 in each yarn 12 to match the peak of human radiation (at 10 μm), thus increasing the resonant Electromagnetic (EM) coupling between the optical nanostructures 16 in adjacent elementary fibers 10 and thus maximizing the infrared emissivity, i.e. enhancing heat transfer under elevated humidity levels/increased perspiration. Thus, in response to ambient humidity level fluctuations (dry, wet) or perspiration levels (low, high), the present meta-cooling fiber 10 is able to self-regulate heat transfer by tuning the infrared emission from the present textile 12 without the cost of additional external energy usage. The humidity responsive self-regulating mechanism of the present invention operates over a wide range of predetermined relative humidity levels, for example, from 5% to 90%, from 10% to 80%, or from 30% to 70%.

The scalable production of the meta-cooling fiber 10 of the present invention is first achieved by the melt spinning process depicted in fig. 2. As shown in fig. 2, the system 20 for the spinning process of the present invention comprises a custom designed dual spinneret 32 uniquely designed (as will be described in further detail herein) and cooperating with a hydrophilic polymer feeder 22 containing a hydrophilic polymer melt 24 and a hydrophobic polymer feeder 26 filled with hydrophobic polymer precursors 30.

Output 37 of feeder 22 and output 39 of feeder 26 form spinneret 32 and are used to extrude hydrophilic polymer 24 and hydrophobic polymer precursor 30, respectively, in a predetermined manner to achieve an alternating fibril configuration. The optical nanostructures 16 used to provide optical coupling between the meta-cooling fibers 10 are pre-blended into the hydrophobic polymer precursor 30 in the feeder 26 at a predetermined concentration.

The hydrophobic polymer precursor 30 containing the optical nanostructures 16 is then spun at the bicomponent spinneret 32 along with the hydrophilic polymer precursor 24 to form the bicomponent cooling fiber 10, as shown in fig. 2. After the bicomponent fibers 10 are formed, they are arranged in a yarn 12 which is wound on a yarn bobbin 21. The yarns 12 are capable of correlating the spatial displacement between adjacent elementary fibers 10 in each yarn by twisting, crimping, self-crimping, texturing, hot water treatment, water vapour heating, air flow and combinations thereof.

Bicomponent spinneret 32 is capable of spinning

polymer precursors

24 and 30/18 in two configurations, including side-by-side configuration 36 shown in fig. 3A, and eccentric core-sheath configuration 38 shown in fig. 3B.

In the exemplary embodiment shown in fig. 3A-3B, carbon nanotubes may be selected as optical nanostructures 16 to be pre-mixed into a hydrophobic polymer precursor 30. The molten polymer compounds 24 and 30 may be arranged in a side-by-side key-lock 36 (fig. 3A) arrangement, or in an eccentric sheath-core configuration 38, depending on which configuration of the spinneret 32 is used.

As shown in fig. 3A, to form a side-by-side arrangement 36, the spinnerets 32 are configured with

feeders

22, 26 having side-by-

side outputs

37, 39 from which the

polymers

26, 30 are extruded in a side-by-side manner to form the fiber arrangement 36. Alternatively, as shown in fig. 3B, the spinneret 32 is configured with the

feeders

22, 26 arranged in a coaxial configuration with an output 37 'in surrounding relation to an output 39' to extrude the

polymers

26, 30 with a core-sheath arrangement 38.

In sheath-core structure 38, the optical nanostructures comprising hydrophobic polymer 30 constitute a core component 40 embedded within a hydrophilic polymer shell 42. This configuration 38 is beneficial to prevent possible loss of the optical nanostructures 16 into the environment. The proportion by weight of the core 40 may range, for example, from 20% to 60% relative to the sheath 42 or from 25% to 40% relative to the sheath 42.

Fig. 4A-4D depict optical and SEM images of cross-sections of exemplary embodiments in a side-by-side configuration 36 (in fig. 4A and 4C) or in an eccentric sheath-core configuration 38 (in fig. 4B and 4D). Although the diameter of the fibril produced in the example shown in fig. 4A to 4D ranges between 10 μm and 20 μm, the diameter of the fibril produced by the method of the present invention may range widely, for example, from 0.1 μm to 50 μm, or from 5 μm to 30 μm, or from 8 μm to 20 μm.

To examine the carbon nanotube doping as an element in the inventive fiber 10, the eccentric sheath-core fiber 38 was sliced and intentionally semi-damaged to expose the core component 40, as shown in fig. 5A-5D. As best seen in fig. 5B and 5D, the carbon nanotubes (optical nanostructures) 16 are uniformly distributed in the core component 40. Such uniform distribution of optical nanostructures 16 in core component 40 demonstrates that the melt spinning process does not adversely affect the incorporation of Carbon Nanotubes (CNTs). The raman spectroscopy pattern shown in fig. 6 further confirms the successful intercalation of CNTs 16 in the polyethylene core component 40 of the resulting meta-cooling fiber 10, exhibiting for CNTs at about 1600cm^-1Characteristic G band of (1).

Fig. 7 is a photograph of the resulting meta-cooling fiber 10 with incremental amounts (0, 100, 250, 500, 750, and 1000ppm) of carbon nanotubes added (doped) in the hydrophobic polymer component. The color of the fibers (left to right) changes from white to gray, indicating increasing doses of carbon nanotubes. The doping of the hydrophobic polymer component with the carbon nanotubes does not interfere with the melt spinning process.

As an example shown in fig. 8A, the manufactured primary cooling fibers may be exposed to a conventional fabric knitting process to produce a single jersey circular knit 14 (shown in fig. 8A) or a double knit 14 (shown in fig. 8B).

Returning again to fig. 1B, 1D, 1F, after spinning, the elementary fibers 10 are arranged in the yarn 12 and set in a straightened configuration. In order to redefine the "closed" (or loose) state of the meta-fibers in dry conditions and the "open" (or tight) state of the meta-fibers in wet conditions, after fiber spinning, a subsequent heat-setting (training) step is performed, where the meta-fibers 10 in the side-by-side configuration 36 or the eccentric configuration 38 are first exposed to high humidity conditions by immersing the fibers 10 in water. The fibers immersed in the water are mechanically distorted to define an "open" (or tight) state under wet conditions. Subsequently, as shown in fig. 9A-9B, the fiber 10 in the original dry/low temperature condition is bent into a bent configuration 46 (fig. 9A) or crimped into a spring-like configuration 48 (fig. 9B), and heat set to define a "closed" (or loose) condition in the dry condition. Thus, after training, when the meta-fiber is exposed to fluctuating environmental conditions, depending on the humidity deviation from the predetermined comfort zone, the meta-fiber changes its configuration, as the thermal training process "dictates", and thus modulates the spacing between adjacent fibers, resulting in changing the EM coupling between the optical nanostructures 16. The modulated EM coupling between the optical nanostructures 16 results in self-adjustment of the IR emissivity to reduce or enhance heat transfer between the wearer's body and the environment.

As shown in fig. 10A to 10C, the behavior of the humidity response was observed from a prototype dual-element cooling fiber 10 having an eccentric sheath-core structure disposed in a yarn 12 made of 70% nylon 6: polyethylene. In the prototype fiber, the polyethylene component (core) of each fiber 10 is hydrophobic, while the nylon 6 component (sheath) is hydrophilic. The two polymers are antagonistic components, i.e., they respond differently to ambient humidity fluctuations, causing one of the materials to expand more than the other, thus transforming the meta-fiber between the "closed" and "open" states defined by the heat-setting step (as illustrated in fig. 9A-9B). This moisture responsive behavior of the elementary fibers 10 further modulates the relative positioning of adjacent elementary fibers 10 in each yarn 12, thus controlling the ir emissivity of the smart fabric 14 containing the elementary fibers 10.

When the environment is dry, the meta-fibers curl to a "closed" state to create a large distance (pitch) between each other, as shown in fig. 1A, 1C, 1E, 10A, and 10C, thus reducing Electromagnetic (EM) coupling between optical nanostructures in adjacent meta-fibers 10. The reduction in EM coupling between the optical nanostructures 16 in the meta-fiber 10 results in reduced heat transport by infrared radiation. When the environment becomes humid, the meta-fibers 10 straighten to an "on" state reducing the distance therebetween, as shown in fig. 1B, 1D, 1F and 10B, thus increasing the Electromagnetic (EM) coupling between the optical nanostructures in adjacent meta-fibers 10, which results in enhanced heat transfer through infrared radiation.

The relationship between the diameter of the yarn formed from the elementary fibers and the relative humidity level is presented in fig. 10D.

The hydrophilic component may be a polymeric material selected from the group of: nylon, nylon 66, nylon 6(PA6), polyurethane, and combinations thereof.

The hydrophobic component may be a polymeric material selected from the group of: polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), and combinations thereof.

The optical nanostructures may be nanomaterials selected from the group of: single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanohorns, carbon fibers, graphene oxide, carbon black, silver nanowires, copper nanowires, silicon nanowires, gold nanoparticles, and combinations thereof.

Results of the experiment

The prototype fibril 10 has been fabricated by spinning two

polymers

24, 30 directly into a bicomponent structure having an eccentric sheath-core configuration 38 or a side-by-side configuration 36, as shown in fig. 2 and 3A-3B. One of the polymer precursors is a hydrophilic precursor 24 having the ability to adsorb and desorb moisture. This property of the hydrophilic material 24 results in changes in volume and relative distance between adjacent fibrils 10 in response to humidity fluctuations. The hydrophobic further polymer 30 is the host for the optical nanostructures 16 homogeneously embedded therein to enable Electromagnetic (EM) coupling between adjacent elementary fibers. In one of the embodiments, CNTs are selected as optical nanostructures, which may be pre-compounded into the hydrophobic polymer 30 prior to spinning. CNTs have high electrical conductivity, chemical stability, mechanical flexibility, and textile fiber-matched length scales, and are therefore good candidates for incorporation into the inventive fibers 10.

In the illustrated experiment, bicomponent meta-fiber 10 was spun through a custom-made spinneret 32 using nylon 6 as the hydrophilic component and polyethylene as the hydrophobic component. Nylon 6 was chosen for its ability to adsorb moisture, while polyethylene was chosen for its low absorption in the infrared range. As confirmed in the optical and SEM images shown in fig. 4A to 4D, the CNT infusion in the polyethylene component did not interfere with the spinning process. In addition, the CNTs remained uniformly distributed in the polyethylene, as evident from the SEM images (fig. 5A to 5D) of the core region of the eccentric sheath-core element fiber, which is further illustrated by showing that at about 1600cm for CNTs^-1The characteristic G band of (a) (depicted in fig. 6) was confirmed.

As an example, meta-cooling fibers 10 having various doses (e.g., 0, 100, 250, 500, 750, and 1000ppm) of CNTs in the eccentric sheath-core structure and core component were configured into yarns 12 at a draw ratio of 3.5:1 and a monofilament fineness of 288. The denier of the resulting meta-fiber (measured to determine fiber thickness) varied from 1.0 to 2.1 depending on the ratio of nylon 6 to polyethylene and the speed of the spinning pump 34 (shown in fig. 2). The color change of the meta-fiber from white to grey (as shown in figure 7) indicates an increased CNT dose in the fiber.

The resulting elementary fibers 10 are arranged in a yarn 12, and the yarn is subsequently knitted into a textile 14 having a single jersey circular knit structure (shown in fig. 8A) or a double knit structure (shown in fig. 8B) with polyester fibers as the supporting substrate. After spinning, the elementary fibers 10 within the yarn 12 are mechanically correlated to reach a straightened configuration. Various CNT doses (ranging from 0 to 1000ppm) were embedded in the core polymer composition. The resulting fibril was strong enough to withstand the knitting process, indicating that the mechanical strength of the fibril was not reduced by the addition of CNTs.

In order to provide self-regulation of infrared emission in the meta-fiber for active modulation of heat transfer from the human body (garment wearer) to the environment in response to humidity level fluctuations, two states of the meta-fiber are defined:

(a) a "closed" state in which the elementary fibers are loosely related to form a large relative distance (pitch) between the fibers 10 within each yarn 12, as shown in fig. 1A, 1C, 1D; and

(b) an "open" state in which the elementary fibers are closely related to form a small relative distance (pitch) 18 between the fibers 10 within the yarn 12, as shown in fig. 1B, 1D, 1F.

In the "closed" state of the elementary fibers, the electromagnetic coupling between adjacent elementary fibers is minimized due to the increased distance 18 between the fibers 10. This configuration results in reduced heat transfer from the wearer's body to the environment, which may be beneficial in dry and/or cold situations.

In contrast, in the "on" state of the meta-fibers, due to the smaller inter-fiber distance 18 (matching the infrared radiation wavelength), the electromagnetic coupling between adjacent meta-fibers 10 is maximized, thus resulting in an enhanced heat transfer from the wearer's body to the environment, which is beneficial in wet and/or hot conditions.

In order to "train" the fibres, i.e. define a "closed" state of the elementary fibres in dry (and/or cold) condition and an "open" state of the elementary fibres in wet (and/or hot) condition, a subsequent heat-setting step is performed, as illustrated in fig. 9A to 9B. Specifically, after the spinning step, the microfibers 10 are first twisted in water to define an "open" state in wet conditions such that they may be bent into a bent configuration 44 or crimped into a spring-like configuration 48, shown in fig. 9A and 9B, respectively. The fibers are also heat set to define a "closed" state in dry conditions (anhydrous). The "closed" state of the fibril is established by heat-setting the fibril in a drying condition having a relative humidity level of less than 20% and a heat-setting temperature ranging between 80 ℃ and 200 ℃.

In an exemplary demonstration, 72 filament yarn using nylon 6 and polyethylene with an eccentric sheath-core structure was processed (trained) to establish "open" and "closed" states. After treatment (training), the element yarn 12 shows a large yarn diameter exposed to a low moisture of 5%, but shrinks to a smaller yarn diameter when the moisture increases to 80%. In particular, the functionality of the present elementary fibers is sufficient at predetermined relative humidity levels ranging from 5% to 90%, from 10% to 80% and from 30% to 70%. Dynamic actuation of the resulting fibril is evidenced by yarn diameter fluctuations in response to humidity level changes and/or due to shrinkage or expansion of sweat being reversible over multiple humidity change cycles.

While the present invention has been described in connection with the specific forms and embodiments thereof, it will be understood that various modifications in addition to those discussed above may be resorted to without departing from the spirit or scope of the invention as defined in the appended claims. For example, functionally equivalent elements may be substituted for those specifically illustrated and described, certain features may be utilized independently of other features, and in certain instances, specific locations of elements, steps or processes may be reversed or inserted without departing from the spirit or scope of the present invention as defined in the appended claims.

Claims

1. A textile comprised of microfibers, comprising:

a plurality of elementary fibers arranged into a yarn, each of the elementary fibers comprising:

the hydrophobic component of the first spinnable polymeric material,

a hydrophilic component of a second spinnable polymeric material, and

a plurality of optical nanostructures embedded in the hydrophobic component;

wherein each of said elementary fibers changes its configuration in response to fluctuations in relative humidity levels, thereby resulting in modulation of inter-fiber spacing within said yarn, thereby changing electromagnetic coupling between said optical nanostructures embedded in said fibers, resulting in modulation of infrared optical emission, followed by active self-regulation of air flow, and/or heat transfer through a smart textile comprised of said elementary fibers.

2. The textile of claim 1, wherein the hydrophobic component and the hydrophilic component are connected in a configuration selected from the group comprising: an eccentric sheath-core configuration, and a side-by-side configuration; wherein in the eccentric sheath-core configuration, the hydrophilic component comprises a core and the hydrophilic component comprises a sheath surrounding the core.

3. The textile of claim 1, wherein the meta-fibers assume a relative disposition with a reduced spacing between adjacent meta-fibers when a moisture level applied to the meta-fibers is above a predetermined relative humidity level, thereby increasing the infrared optical emission to enhance heat transfer through the smart textile,

wherein when said moisture level applied to said meta-fibers is below said predetermined relative humidity level, said meta-fibers assume a relative disposition with increased spacing between adjacent meta-fibers, thereby reducing said infrared optical emission to reduce heat transfer through said smart textile.

4. The textile according to claim 1, wherein the predetermined range of relative humidity levels is 5% to 90%, or 10% to 80%, or 30% to 70%.

5. A textile according to claim 1 wherein in response to modulation of the spacing between adjacent elementary fibres, the configuration of the yarns is reversibly changed by contraction or expansion of the yarns in response to the fluctuations in the relative humidity level, exposure to perspiration or a combination thereof.

6. A textile according to claim 1, wherein the diameter of the primary fibres ranges from 0.1 to 50 μ ι η, or from 5 to 30 μ ι η, or from 8 to 20 μ ι η.

7. The textile according to claim 2, wherein the proportion by weight of the core ranges from 20% to 60% with respect to the sheath, or from 25% to 40% with respect to the sheath.

8. The textile of claim 2, wherein the hydrophilic component is a polymeric material selected from the group consisting of: nylon, nylon 66, nylon 6(PA6), polyurethane, and combinations thereof.

9. The textile of claim 1, wherein the hydrophobic component is a polymeric material selected from the group consisting of: polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polybutylene terephthalate (PBT), and combinations thereof.

10. The textile of claim 1, wherein the optical nanostructures comprise nanomaterials selected from the group consisting of: single-walled carbon nanotubes, double-walled carbon nanotubes, few-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanohorns, carbon fibers, graphene oxide, carbon black, silver nanowires, copper nanowires, silicon nanowires, gold nanoparticles, and combinations thereof.

11. The textile according to claim 1, wherein the optical nanostructures are pre-doped in the polymeric material of the hydrophobic component by compounding.

12. The textile of claim 1, wherein the optical nanostructures have a weight in a range selected from the group consisting of: 0.0025 to 0.03%, 0.005 to 0.05%, and 0.01 to 0.5% by weight of the hydrophobic component in the meta-fiber.

13. The textile according to claim 2, wherein the weight of the optical nanostructures is in the range of 10-1000ppm with respect to the core in the meta-fiber.

14. The textile of claim 2, wherein the fibril comprises Polyethylene (PE) and carbon nanotubes in the core and nylon 6(PA6) in the sheath.

15. The textile of claim 2, wherein the fibril comprises Polyethylene (PE) and graphene oxide in the core and nylon 6(PA6) in the sheath.

16. The textile of claim 2, wherein the meta-fibers comprise polyethylene terephthalate (PET) and carbon nanotubes in the core and nylon 6(PA6) in the sheath.

17. A method of making a yarn from a fibril having moisture responsive behavior and self-regulating ir emissivity comprising:

(a) compounding optical nanostructures into a hydrophobic polymer, thereby forming a hydrophobic component of the fibril;

(b) forming the meta-fiber by melt spinning the hydrophobic component containing the optical nanostructures pre-doped with a hydrophilic component through a twin spinneret to form a fiber configuration selected from the group consisting of: an eccentric sheath-core configuration, and a side-by-side configuration;

(c) arranging a plurality of said elementary fibres in said yarn in relation to enable spatial displacement between adjacent elementary fibres in said yarn; and

(d) heat-setting the yarn to establish the "open" and "closed" states of the fibril under dry/cold and wet/hot conditions, respectively.

18. The method of claim 17, wherein in said step (b), said eccentric sheath-core configuration comprises a sheath formed with said hydrophilic component and a core formed with said hydrophobic component and said optical nanostructure, said sheath disposed in surrounding relation to said core.

19. The method of claim 17, wherein in step (c), the spatial correlation between adjacent fibrils is by twisting, crimping, self-crimping, texturing, hot water treatment, water vapor heating, air purging, and combinations thereof.

20. The method of claim 17, further comprising the steps of:

in said step (d), said "closed" state of said meta-fibres is established by heat-setting said meta-fibres in dry conditions having a relative humidity level below 20% and having a heat-setting temperature ranging between 80 ℃ and 200 ℃.

21. A method of making a fibril having moisture responsive behavior and self-regulating ir emissivity comprising:

(a) compounding an optical nanostructure into a hydrophobic polymer, thereby forming a hydrophobic compound; and

(b) producing a fibril by melt spinning the hydrophobic component and a hydrophilic component comprising a hydrophilic polymer through a twin spinneret, thus configuring the fibril in a spinning configuration selected from the group consisting of: an eccentric sheath-core configuration, and a side-by-side configuration.

22. The method of claim 21, wherein in step (b) the eccentric sheath-core configuration of the meta-fiber comprises a sheath formed by the hydrophilic component and a core formed by the hydrophobic component embedded with the optical nanostructures.